Axial flow gas turbine engines are used to power modern aircraft. These gas turbine engines typically include a compression section, a combustion section, and a turbine section. A flow path for working medium flow gases extends axially through the sections of the engine.
As the gases are flowed along the flow path, the working medium gases are compressed in the compression section. The working medium gases are flowed to the combustion section where they are mixed with fuel. The gases and fuel are burned to add energy to the gases. The gases are expanded through the turbine section to produce useful work to power the compression section and, in the case of aircraft engines, to power the aircraft.
The working medium gases are burned with the fuel in a combustion chamber. The combustion chamber provides a combustion zone for the gases and shields the interior of the engine from radiation heat transfer from the gases. One typical example of such a combustion chamber is shown in U.S. Pat. No.: 4,870,818 entitled Fuel Nozzle Guide Structure and Retainer for a Gas Turbine Engine issued to William G. Suliga, and assigned to the assignee of the present invention.
In Suliga, the combustion chamber includes an inner liner 14 and an outer liner 16. A dome-shaped head assembly 18 extends circumferentially about the upstream end of the combustion chamber. The head includes a circumferentially extending dome 20 which is a major element of the combustion chamber. The dome has a plurality of openings which adapt the combustion chamber to receive air from the compressor and to receive a fuel supply means such as a fuel nozzle. The head includes a generally planar bulkhead 28 which extends from the inner liner to the outer liner of the combustion chamber. The bulkhead has a plurality of openings, each associated with a corresponding opening in the dome, which permit a fuel nozzle to extend into the combustion chamber. Each opening in the bulkhead has a reference axis A.sub.b.
The combustion chamber also includes minor elements such as a fuel nozzle guide 44. The fuel nozzle guide is disposed in an associated opening in the bulkhead. The fuel nozzle guide moves with the nozzle and slides with respect to the bulkhead to accommodate thermal growth of the components which might occur at different rates for the components. A hole through the guide adapts the guide to receive a fuel nozzle.
The fuel nozzle guide includes a heat shield 46 extending parallel to the bulkhead, that shields the bulkhead from the combustion zone. The fuel nozzle guide also has a member which extends axially from the heat shield to the upstream side of the bulkhead. A retainer ring 52 is attached to the upstream end of the fuel nozzle guide and slideably engages the upstream side of the bulkhead to axially trap the fuel nozzle guide on the bulkhead. A clearance gap is provided between the bulkhead and the fuel nozzle guide to allow for the slideable movement of the fuel nozzle with respect to the bulkhead. In particular, this slideable movement accommodates differences in thermal expansion between the bulkhead, the fuel nozzle (and of course the fuel nozzle guide), and the inner and outer liner during operative conditions of the engine.
Another embodiment of a combustion chamber is shown in U.S. Pat. No.: 4,934,145 entitled Combustor Bulkhead Heat Shield Assembly issued to Melvin H. Zeisser and assigned to the assignee of the present invention. A similar construction is shown in U.S. Pat. No.: 4,914,918 entitled Combustor Segmented Deflector issued to Dennis J. Sullivan and assigned to the assignee of the present invention.
In the Zeisser embodiment, the fuel nozzle guide 86 has a heat shield portion. The heat shield portion extends radially and parallel to the bulkhead, to form a cooling air plenum between the bulkhead and the fuel nozzle. A separate heat shield is disposed in the plenum. The separate heat shield: bounds a first passage having one closed end which extends between the heat shield and the bulkhead; and, bounds a second downstream passage having two open ends which extends between the heat shield and the fuel nozzle guide. These passages extend radially to duct cooling air through this region of the combustion chamber. Thus, the innermost end of the heat shield extends to seal the upstream radially extending passage from the plenum.
Accordingly, a plurality of cooling air holes 46 through the bulkhead are required to provide cooling air to the axially upstream passage. The holes in the bulkhead are sized to provide impingement cooling to the heat shield. The holes are angled toward the closed end of the upstream passage to direct the air radially inwardly. The flow of cooling air is ducted in the radially outward direction past the impingement jets to the perimeter of the heat shield and thence is exhausted into the combustion chamber. The axially downstream passage between the heat shield and the heat shield of the fuel nozzle guide is supplied with cooling air which is ducted through passages extending through the fuel nozzle guide.
The above art notwithstanding, scientists and engineers are seeking to develop bulkhead and fuel nozzle guide assemblies which provide for flexibility in design and duct cooling air to appropriate locations in the bulkhead assembly.